"During the investigation of the sabotage planned in May 2023 to blow up long-range aircraft stationed at the Severny airfield in the Ivanovo region, it became known about the plans of the Main Intelligence Directorate of the Ukrainian Defense Ministry to commit a terrorist act in Russia using the so-called 'dirty bomb,'" the FSB said in a statement.
Ukraine planned to deliver and plant "dirty bombs" equipped with delay timers to simultaneously blow up and render the area uninhabitable, the statement read.
The coordination of the use of light aircraft was entrusted to a military unit, codenamed "Legion," which is part of the Main Intelligence Directorate of the Ministry of Defense of Ukraine.
"Since the beginning of the year, this unit has planned and carried out five flights to Russia, during which fuel and energy complex facilities in the regions of Russia bordering Ukraine were damaged," the FSB said.
As a result of special operations by the FSB, two pilots of light aircraft of Ukraine's new military intelligence unit were detained, the statement read, adding that they confessed to committing and planning terrorist attacks in Russia.